System and method for machining a slot in an inner surface of a casing for a gas turbine engine

ABSTRACT

A milling device for machining a slot into an inner surface of a casing for a gas turbine engine. The milling device includes a frame assembly including multiple structural guides configured to engage structural features on the inner surface of the casing to maintain an axial position of the milling device relative to a longitudinal axis of the casing. The milling device also includes a milling cutter coupled to the frame assembly. The milling device is configured to be displaced in a circumferential direction relative to the longitudinal axis to machine the slot, via the milling cutter, along the inner surface of the casing in the circumferential direction.

BACKGROUND

The subject matter disclosed herein relates to a gas turbine system and,more particularly, to a system and method for machining a slot into acasing of the gas turbine system.

Gas turbines are used to generate power for various applications.Typically, testing and validation are performed on these gas turbinesprior to their utilization (e.g., in a power generating station).Effective testing and validation can increase the efficiency of andproductivity of the gas turbines as well as the power generatingstation. However, the installation of equipment for performing thetesting and validation on the gas turbine engine may be labor intensiveand time consuming.

BRIEF DESCRIPTION

Certain embodiments commensurate in scope with the originally claimedsubject matter are summarized below. These embodiments are not intendedto limit the scope of the claimed subject matter, but rather theseembodiments are intended only to provide a brief summary of possibleforms of the subject matter. Indeed, the subject matter may encompass avariety of forms that may be similar to or different from theembodiments set forth below.

In one embodiment, a milling device for machining a slot into an innersurface of a casing for a gas turbine engine is provided. The millingdevice includes a frame assembly including multiple structural guidesconfigured to engage structural features on the inner surface of thecasing to maintain an axial position of the milling device relative to alongitudinal axis of the casing. The milling device also includes amilling cutter coupled to the frame assembly. The milling device isconfigured to be displaced in a circumferential direction relative tothe longitudinal axis to machine the slot, via the milling cutter, alongthe inner surface of the casing in the circumferential direction.

In another embodiment, a sled milling device is provided. The sledmilling device includes a frame assembly and a milling cutter coupled tothe frame assembly. The sled milling device also includes a bearingsupport configured to interface with an inner surface of casing of a gasturbine engine, to provide a supporting force in a directionperpendicular to a longitudinal axis of the casing, and to enablemovement of the sled milling device in a circumferential directionrelative to the longitudinal axis. The sled milling device is configuredto be displaced in the circumferential direction to machine a slot, viathe milling cutter, along the inner surface of the casing in thecircumferential direction.

In a further embodiment, a milling system for machining a slot into aninner surface of a casing for a gas turbine engine is provided. Themilling system includes a sled milling device that includes a frameassembly and a milling cutter. The sled milling device is configured tobe displaced in a circumferential direction relative to a longitudinalaxis of the casing to machine the slot, via the milling cutter, alongthe inner surface of the casing in the circumferential direction,wherein the frame assembly is configured to be interchangeably coupledto different sets of structural guides. Each set of structural guidesincludes a different size, shape, or a combination thereof, to enablethe sled milling device to engage different structural features on theinner surface of the casing to maintain an axial position of the millingdevice relative to a longitudinal axis of the casing. The milling systemalso includes the different sets of structural guides.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the present subjectmatter will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a block diagram of an embodiment of a turbine system having anaeromechanics measurement system;

FIG. 2 is a cross-sectional side view of an embodiment of the turbinesystem, as illustrated in FIG. 1, with the aeromechanics measurementsystem;

FIG. 3 is a perspective view of an embodiment of an inner surface of aportion of a casing (e.g., compressor casing) for a gas turbine enginehaving multiple circumferential tracks;

FIG. 4 is a perspective view of an embodiment of a portion of acircumferential track embedded in the inner surface of the casing, takenwithin line 4-4 of FIG. 3;

FIG. 5 is a side schematic view of an embodiment of a milling systembeing utilized to machine a slot along an inner surface of a casing;

FIG. 6 is a perspective view of an embodiment of a milling device beingutilized to machine a slot along an inner surface of a casing;

FIG. 7 is a top perspective view of the milling device being utilized tomachine the slot in FIG. 6;

FIG. 8 is a side cross-sectional view of the milling device beingutilized to machine the slot in FIG. 6;

FIG. 9 is a front perspective view of an embodiment of a milling devicebeing utilized to machine a slot along an inner surface of a casing;

FIG. 10 is a rear perspective view of the milling device being utilizedto machine the slot in FIG. 9;

FIG. 11 is a side view of the milling device being utilized to machinethe slot in FIG. 9;

FIG. 12 is a side view of a portion of the milling device of FIG. 9(e.g., of a structural guide); and

FIG. 13 is a flow chart of a method for utilizing a milling device tomachine a slot along an inner surface of a casing.

DETAILED DESCRIPTION

One or more specific embodiments will be described below. In an effortto provide a concise description of these embodiments, not all featuresof an actual implementation are described in the specification. Itshould be appreciated that in the development of any such actualimplementation, as in any engineering or design project, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which may vary from one implementation toanother. Moreover, it should be appreciated that such a developmenteffort might be complex and time consuming, but would nevertheless be aroutine undertaking of design, fabrication, and manufacture for those ofordinary skill having the benefit of this disclosure.

When introducing elements of various embodiments of the presentdisclosure, the articles “a,” “an,” “the,” and “said” are intended tomean that there are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements.

Embodiments of the present disclosure include a milling system formilling a slot (e.g., circumferential slot) into an inner surface ordiameter of a casing (e.g., compressor casing) of a gas turbine engine.The slot extends in a circumferential direction relative to alongitudinal axis of the casing or gas turbine engine. The slot isconfigured to receive a circumferential track that defines a cavity forreceiving a measurement system (e.g., having a plurality of sensors) forvalidating the operation of the gas turbine engine. The milling systemincludes a milling device or tool (e.g., a sled-style milling device ortool) that includes a frame assembly and a milling cutter (e.g., endmill cutter or bit) coupled to the frame assembly. The frame assemblyincludes or is coupled to structural guides that are configured toengage structural features (e.g., slots or retention lobes on structuralfeatures (e.g., protrusions) that define slots for retaining compressorstator vanes) on the inner surface of the casing to maintain an axialposition of the milling device relative to the longitudinal axis. Theframe assembly may be interchangeably coupled to different sets ofstructural guides (e.g., where the size and/or shape of the structuralguides vary between sets), where each set of structural guides isdesigned to engage structural features on the inner surface of thecasing having different sizes and/or shapes. The milling device isconfigured to be displaced (e.g., via a force applied by an operator) inthe circumferential direction along the inner surface of the casing tomachine the slot via the milling cutter. In certain embodiments, themilling device includes a bearing support that interfaces with the innersurface of the casing that provides a supporting force in a directionperpendicular to the longitudinal axis while enabling movement of thesled milling device in a circumferential direction. The architecture ofthe milling device enables it to be adapted to and utilized on the innersurface of any casing (e.g., circular or semi-circular casing) of a gasturbine engine that has casing features near an area to be milled. Themilling device also enables precise alignment of the milling or cuttingtool to create the circumferential slot utilizing the casing features.The milling device may even be utilized on casings that are damaged,warped, or worn. In addition, the milling device is highly transportabledue to its small size and light weight and may be utilized by a singleperson to machine the slot.

Turning to the figures, FIG. 1 is a block diagram of an embodiment of aturbine system 10 having a gas turbine engine 11. For reference, the gasturbine engine 11 may extend in axial direction 30 (e.g., relative to alongitudinal axis 36 of gas turbine engine 11 or casing 42, see FIG. 2),a radial direction 32 toward or away from the longitudinal axis 36, anda circumferential direction 34 around the longitudinal axis 36. Thedisclosed turbine system 10 employs a measurement system 13 (e.g.,aerodynamics measurement system) whose installation and use are madepossible due to a milling system described in greater detail below. Themeasurement system 13 may include a sensor assembly having a pluralityof sensors that measure a variety of operational parameters utilized toprovide baseline data in validating the operation of the gas turbineengine 11. The measurement system 13 operates independent of the controlsystem for the gas turbine engine 11. The number of sensors may rangefrom dozens to a hundred to thousands of sensors. At least some of thesensors may employ optics and/or fiber optics. The operationalparameters measured may include blade tip timing (e.g., fordisplacement, stress, frequency, etc.), blade tip clearance,temperature, dynamic pressure, static pressure, rotor vibration, stalldetection, and rotor speed.

The sensor assembly is disposed within a space or cavity defined by acircumferential track embedded within a circumferential slot along aninner surface or diameter of a casing (e.g., compressor casing) of thegas turbine engine 11. The circumferential track and slot extends in thecircumferential direction 34 relative to a longitudinal axis 36 of thegas turbine engine 11. In certain embodiments, the casing may include aplurality of circumferential tracks (and circumferential slots) spacedapart from each other in the axial direction 30. In certain embodiments,the measurement system 13 may include a plurality of sensor assemblieseach having a plurality of sensors, where the sensors assemblies may beinserted into multiple circumferential tracks.

The circumferential slots need to have a certain profile to receive theembedded sensor track system. A milling system that includes a millingdevice (e.g., a sled-style milling system) is utilized to machine thecircumferential slots. The milling device utilizes existing casingstructural features (e.g., protrusions that define retention lobes orslots for retaining compressor stator vanes) on the inner surface of thecasing near the area to be milled or machined as both a support for themilling device and a guide for the path of the milling device. Themilling device includes a frame assembly and a milling cutter (e.g., endmill cutter or bit) coupled to the frame assembly. The type of cutterutilized with the milling device is interchangeable. The frame assemblyincludes or is coupled to structural guides that are configured toengage the structural features on the inner surface of the casing tomaintain an axial position of the milling device relative to thelongitudinal axis. The frame assembly may be interchangeably coupled todifferent sets of structural guides (e.g., where the size and/or shapeof the structural guides vary between sets), where each set ofstructural guides is designed to engage structural features on the innersurface of the casing having different sizes and/or shapes. Thus, themilling device may be utilized to create different types of slotprofiles. The adaptability of the milling device enables it to beutilized on damaged, warped, or worn casings. In addition, the millingdevice is configured to be displaced (e.g., via a force applied by anoperator) in the circumferential direction along the inner surface ofthe casing to machine the slot via the milling cutter. In certainembodiments, the milling device includes a bearing support thatinterfaces with the inner surface of the casing that provides asupporting force in a direction perpendicular to the longitudinal axiswhile enabling movement of the sled milling device in a circumferentialdirection. The milling device may be utilized on any type of circular orsemi-circular casing (e.g., compressor casing, turbine casing, etc.).

The turbine system 10 may use liquid or gas fuel, such as natural gasand/or a synthetic gas, to drive the turbine system 10. As depicted, oneor more fuel nozzles 12 intake a fuel supply 14, partially mix the fuelwith air, and distribute the fuel and the air-fuel mixture into acombustor 16 where further mixing occurs between the fuel and air. Theair-fuel mixture combusts in a chamber within the combustor 16, therebycreating hot pressurized exhaust gases. The combustor 16 directs theexhaust gases through a turbine 18 toward an exhaust outlet 20. As theexhaust gases pass through the turbine 18, the gases force turbineblades to rotate a shaft 22 along an axis of the turbine system 10. Asillustrated, the shaft 22 is connected to various components of theturbine system 10, including a compressor 24. The compressor 24 alsoincludes blades coupled to the shaft 22. As the shaft 22 rotates, theblades within the compressor 24 also rotate, thereby compressing airfrom an air intake 26 through the compressor 24 and into the fuelnozzles 12 and/or combustor 16. The shaft 22 may also be connected to aload 28, which may be a vehicle or a stationary load, such as anelectrical generator in a power plant or a propeller on an aircraft, forexample. The load 28 may include any suitable device capable of beingpowered by the rotational output of turbine system 10.

FIG. 2 is a cross-sectional side view of an embodiment of the gasturbine engine 11 as illustrated in FIG. 1. The gas turbine engine 11has a longitudinal axis 36. In operation, air enters the gas turbineengine 11 through the air intake 26 and is pressurized in the compressor24. The compressed air then mixes with gas for combustion within thecombustor 16. For example, the fuel nozzles 12 may inject a fuel-airmixture into the combustor 16 in a suitable ratio for optimalcombustion, emissions, fuel consumption, and power output. Thecombustion generates hot pressurized exhaust gases, which then driveturbine blades 38 within the turbine 18 to rotate the shaft 22 and,thus, the compressor 24 and the load 28. The rotation of the turbineblades 38 causes a rotation of the shaft 22, thereby causing blades 40(e.g., compressor blades) within the compressor 24 to draw in andpressurize the air received by the intake 26.

As depicted, a casing 42 (e.g., compressor casing) surrounds the blades40 (and stator vanes) of the compressor 24. The casing 42 may includemultiple sections (e.g., two halves) that together extend completelyabout the longitudinal axis 36 to define the interior of the compressor24. A circumferential track 44 is embedded within a slot 45 along aninner surface or diameter 46 of the casing 42. The measurement system 13includes the sensor assembly 48 having the plurality of sensors disposedwithin a space or cavity defined between the circumferential track 44and the inner diameter 46 of the casing 42. The circumferential track 44is axially 30 disposed between the rows of stator vanes (not shown) sothat the circumferential track 44 and, thus, the sensors of the sensorassembly 48 are in the plane of (and axially 30 aligned with) therotating blades 40. The circumferential track 44 extends in thecircumferential direction 34 at least a portion about the inner diameter46 of the casing 42. In certain embodiments, the circumferential track44 extends about the entire inner diameter 46 of the casing 42.

FIG. 3 is a perspective view of an embodiment of the inner surface 46 ofa portion of the casing 42 (e.g., compressor casing) for the gas turbineengine 11 having multiple circumferential tracks 44. The stator vanesand the respective slots for receiving them are not shown. In certainembodiments, the number of circumferential tracks 44 may correspond tothe number of stages of blades 40. In other embodiments, the number ofcircumferential tracks 44 may be less than or greater than the number ofstages of blades 40. As depicted, the circumferential tracks 44 areaxially 30 spaced apart from each other relative to the longitudinalaxis 36. As mentioned above, the circumferential track 44 is axially 30disposed between the rows of stator vanes so that the circumferentialtrack 44 and, thus, the sensors of the sensor assembly 48 are in theplane of (and axially 30 aligned with) the rotating blades 40. Thecircumferential track 44 extends in the circumferential direction 34 atleast a portion about the inner diameter 46 of the casing 42. In certainembodiments, the circumferential track 44 extends about the entire innerdiameter 46 of the casing 42.

In certain embodiments, the circumferential track 44 is a single segment50 as depicted with circumferential track 52. In other embodiments, thecircumferential track 44 may include multiple segments 50 as depictedwith circumferential track 54. Each circumferential track 44 includesopenings 56 that enable the sensors of the sensor assembly 48 to facetoward an interior of the compressor 24 (e.g., toward the blades 40)when the sensor assembly 48 is properly inserted within the spacedefined by the circumferential track 44 and the inner diameter 46 of thecasing 42. The openings 56 may include larger openings 58 and smalleropenings 60 sized for specific sensors. In certain embodiments, theopenings 56 may be circumferentially 34 aligned or axially 30 aligned.As depicted in FIG. 4, a space or cavity 62 is defined between thecircumferential track 44 and the inner surface 46 of the casing 42. Thesensor assembly 48 may be inserted into and/or removed from the space orcavity 62.

FIG. 5 is a side schematic view of an embodiment of a milling system 64(e.g., machining system) being utilized to machine the slot 45 along theinner surface 46 of the casing 42. As depicted, the inner surface 46 ofthe casing 42 includes structural features 66. These structural featuresinclude slots 68 extending in the circumferential direction 34 forretaining stator vanes (e.g., compressor stator vanes) defined betweenprotrusions 70. The protrusions 70 include retention lobes, slots, orrecesses 72 that are utilized in retaining the stator vanes within theslots 68. These structural features 66 may vary in size, shape, orspacing between each other. The milling system 64 utilizes thestructural features 66 in both supporting and guiding the milling system64 in machining the slot 45.

The milling system 64 includes a milling device or tool 74 for machining(e.g., routing, grinding, milling, etc.) the slot 45 (e.g., within theprotrusion 70). The milling device 74 includes a frame assembly 76 and amilling cutter or bit 78 (e.g., end mill cutter) coupled to the frameassembly 76 that machines the slot 45. The milling device 74 may beinterchangeably coupled to different milling cutters (e.g., roughing endmill, finishing end mill, square end mill, ball end mill, etc.). Themilling cutter 78 may be coupled to an electric motor drive coupled to apower source (not shown). As depicted, the frame assembly 76 includes aplate 80 and a pair of rails 82 flanking the plate 80. The plate 80 ishorizontally oriented relative to the pair of rails 82 (which extendvertically in the radial direction 32). The milling cutter 78 is coupledto the plate 80. In certain embodiments, the position of the millingcutter 78 along the plate 80 may be adjusted (e.g., to change an axialposition of the milling cutter 78 relative to the longitudinal axis 36).The frame assembly 76 is adjustable in size to account for thestructural features 66 on the inner surface 46 of the casing 42. Inparticular, a distance 84 between the rails 82 is adjustable toaccommodate for a width 86 of the protrusion 70. As depicted, themilling device 74 extends over the protrusion 70. In certainembodiments, the milling device 74 extends between multiple adjacentprotrusions 70.

The milling system 64 includes structural guides 88 coupled to the rails82. The structural guides 88 are configured to engage the structuralfeatures 66 (e.g., retention lobes 72) on the protrusion 70 to maintainan axial position (e.g., relative to the longitudinal axis 36) of themilling device 74. As depicted, the structural guides 88 are disposed oninner surfaces 90 of the rails 82 to engage the retention lobes 72disposed on opposite sides of the same protrusion 70. In certainembodiments, the structural guides 88 may be disposed on an outersurface of the rails 82 or another portion of the frame assembly 76 toengage a respective retention lobe 72 on different protrusions 70 (e.g.,where the different protrusions 70 flank the protrusion 70 where theslot 45 is to be machined). The milling system 64 may include differentsets of structural guides 88. Each set of structural guides 88 may bespecifically shaped or sized to different structural features 66 ofdifferent sizes and/or shapes. The milling device 74 may beinterchangeably coupled to the different sets of structural guides 88.This (along with the adjustability of the frame assembly 76) enables themilling device 74 to be coupled to different structural features 66 onany type of circular or semi-circular casing 42 (including those withinner surfaces 46 that are damaged, warped, or worn).

The milling device 74 also includes frictionless support structures 92that interface with (e.g., contact) the inner surface 46 of the casing42 (e.g., top of protrusion 70). In certain embodiments, thefrictionless support structures 92 act as bearing support. Thefrictionless support structures 92 provide a supporting force in adirection (e.g., radial direction 32) perpendicular to the longitudinalaxis 36. In addition, the frictionless support structures 92 enablemovement (as indicated by arrows 94) in the circumferential direction 34along the inner surface 46 of the casing 42 in response to a forceexerted by an operator. Thus, the milling device 74 acts as a sled-stylemilling device. The small size and the light weight of the millingdevice 74 enable the milling device 74 to be utilized by a single personto machine the slot 45. In certain embodiments, the frictionless supportstructures 92 may include spring loaded frictionless pins (e.g., made ofplastic, graphite, or some other frictionless material). As depicted,the frictionless support structures 92 extend from a bottom of the plate80. In other embodiments, the frictionless support structures 92 mayextend from another portion of the frame assembly 76 (e.g., the rails82).

FIGS. 6-8 depict a milling device 96 being utilized to machine the slot45 along the inner surface 46 of the casing 42. The casing 42 and itsfeatures are as described with reference to FIG. 5. The milling device96 includes a frame assembly 98 and a milling cutter or bit 100 (e.g.,end mill cutter) coupled to the frame assembly 98 that machines the slot45. The milling device 96 may be interchangeably coupled to differentmilling cutters (e.g., roughing end mill, finishing end mill, square endmill, ball end mill, etc.). The milling cutter 100 may be coupled to anelectric motor drive coupled to a power source (not shown) disposedwithin the housing 102.

The frame assembly 98 includes a plate or bracket 104 verticallyoriented in the radial direction 32. The milling device 96 is coupled tothe support plate 104 via a plate 106. A pair of support arms or rails108 is coupled to the plate 104 via a pair of respective supportbrackets 110. The support arms 108 are coupled to the support brackets110 via fasteners 111 (e.g., bolts). The supports arms 108 and thesupport brackets 110 flank the milling cutter 100 and extend away fromthe plate 104. The support brackets 110 are coupled via fasteners (notshown) to respective slots 112 within the plate 104 that flank the plate106. A width or distance 114 between the support arms 108 can beadjusted by altering the position of the supports arms 108 in the axialdirection 30 along the slots 112. The support arms 108 also includeslots 116 that enable the position of the supports arms 108 to beadjusted radially 32 relative to the support brackets 110 and, thus, toalter a vertical position of the milling cutter 100 and a depth 118 ofthe slot 45.

Each support arm 108 is coupled to rollers 120. A respective roller 120is coupled to the opposing inner surfaces of each end 122 of the supportarms 108. Each support bracket 110 is coupled to a support structure126. The support structures 126 provide a supporting force in adirection (e.g., radial direction 32) perpendicular to the longitudinalaxis 36. Each support structure 126 includes a stem portion 128 and anend portion 130. The stem portion 128 is configured to move in theradial direction 32 within a recess 131 within the support structure 126to enable the support structure 126 to adjust to differences in heightof the structural features 66 along the inner surface 46 of the casing42 (e.g., in the axial direction). As depicted in FIG. 8, the supportstructures 126 are extended from their respective support brackets 110at different lengths to accommodate a difference in height betweenadjacent retention lobes 72 on the protrusion 70. The end portion 130includes a flange or structural guide 132 that engages or fits withinthe retention lobe 72. The flange 132 enables the milling device 96 tomaintain an axial position relative to the longitudinal axis 36. The endportion 130 is frictionless. The frictionless end portions 130 (alongwith the rollers 120) enable movement in the circumferential direction34 along the inner surface 46 of the casing 42 in response to a forceexerted by an operator. Thus, the milling device 96 acts as a sled-stylemilling device. The milling device 96 may be interchangeably coupled todifferent sets of end portions 130. Each set of end portions 130 mayinclude structural guides 132 that are specifically shaped or sized toengage structural features 66 of different sizes and/or shapes. This(along with the adjustability of the frame assembly 98) enables themilling device 96 to be coupled to different structural features 66 onany type of circular or semi-circular casing 42 (including those withinner surfaces 46 that are damaged, warped, or worn).

FIGS. 9-12 depict a milling device 134 being utilized to machine theslot 45 along the inner surface 46 of the casing 42. The casing 42 andits features are as described with reference to FIG. 5. The millingdevice 134 includes a frame assembly 136 and a milling cutter or bit 138(e.g., end mill cutter) coupled to the frame assembly 136 that machinesthe slot 45. The milling device 134 may be interchangeably coupled todifferent milling cutters (e.g., roughing end mill, finishing end mill,square end mill, ball end mill, etc.). The milling cutter 138 may becoupled to an electric motor drive coupled to a power source (not shown)disposed within the housing 140. The milling device 134 may include oneor more handles 142 for the operator to displace the milling device inthe circumferential direction 34. One of the handles 142 may include anactuator 144 (e.g., trigger) for actuating the milling cutter 138. Themilling device 134 may also include instrumentation 146 for inspectionof the machining of the slot 45.

The frame assembly 136 includes a pair of bars 148 and a first pair ofrails 150 and a second pair of rails 152 coupled (e.g., clamped) to thebars 148 via fasteners 154, 156 (e.g., bolts). The bars 148 extend inthe axial direction 30 and the rails 150, 152 in the circumferentialdirection 34. The first pair of rails 150 flank the second pair of rails152. The rails 150, 152 are adjustable in the axial direction 30 alongthe bars 148. This enables the frame assembly 136 to be adjusted to thestructural features 66 along the inner surface 46 of the casing 42.

A plate 158 is coupled to the first pair of rails 150 via fasteners 160(e.g., bolts). A plate 162 is coupled the plate 158 via brackets 164fastened to the plate 158 via fasteners 166 (e.g., bolts). The millingcutter 138 is coupled to a drive (not shown) within the housing 140 thatextends through both of the plates 158, 162. The milling cutter 138 isdisposed within a slot 168 on the plate 158. The slot 168 extends in theaxial direction 30. Each plate 158, 162, is coupled to a respectivethreaded receptacle 170, 172. The threaded receptacles 170, 172 arevertically aligned with each other in the axial direction 30. Anactuator 174 (e.g., knob screw) extends through the receptacles 170,172. The actuator 174 includes a knob 176 and a threaded portion 178.The threaded portion 178 interfaces within the threaded portion of thereceptacles 170, 172. Actuation (e.g., rotation) of the actuator 174adjusts a position of the plate 162 with respect to the plate 158 in theaxial direction 30, which adjusts the axial position of the millingcutter 138 within the slot 168.

As shown in FIG. 10, the milling device 134 includes structural guides180 coupled to the rails 152. The number of structural guides 180 oneach rail 152 may vary (e.g., 2, 3, 4, 5, or more structural guides180). The structural guides 180 are configured to engage the structuralfeatures 66 (e.g., retention lobes 72) on the protrusion 70 to maintainan axial position (e.g., relative to the longitudinal axis 36) of themilling device 134. The structural guides 180 are respectively coupledto bracket supports 182 that are coupled to the rails 152 via fasteners184 (e.g., bolts). As depicted, the structural guides 180 are disposedon outer surfaces 186 of the rails 82 to engage the retention lobes 72disposed on the protrusions 70 flanking the protrusion 70 where the slot45 is being machined. As depicted, the structural guide 180 has anL-shape. The milling device 134 may be interchangeably coupled to thedifferent sets of structural guides 180. Each set of structural guides180 may be specifically shaped or sized to different structural features66 of different sizes and/or shapes. This (along with the adjustabilityof the frame assembly 136) enables the milling device to be coupled todifferent structural features 66 on any type of circular orsemi-circular casing 42 (including those with inner surfaces 46 that aredamaged, warped, or worn).

The milling device 134 also includes frictionless support structures 188that interface (e.g., contact) with the inner surface 46 of the casing42 (e.g., within slots 68). The frictionless support structures 188 arespring loaded frictionless pins 190 (e.g., made of plastic, graphite, orsome other frictionless material). As depicted, the frictionless supportstructures 188 extend from a bottom surface 192 of the rails 152. Thefrictionless support structures 188 provide a supporting force in adirection (e.g., radial direction 32) perpendicular to the longitudinalaxis 36. In addition, the frictionless support structures 188 are wearcompensating. In particular, the springs of the spring loadedfrictionless pins 190 enables the frictionless support structures 188 towear or be consumed without changing the setup or precision of thesystem. Further, the frictionless support structures 188 enable movementin the circumferential direction 34 along the inner surface 46 of thecasing 42 in response to a force exerted by an operator. Thus, themilling device 134 acts as a sled-style milling device. The small sizeand the light weight of the milling device 134 enables the millingdevice 74 to be utilized by a single person to machine the slot 45.

FIG. 13 is a flow chart of a method 194 for utilizing a milling device(e.g., milling devices 74, 96, 134) to machine a slot along an innersurface of a casing of a gas turbine engine. The method 194 includescoupling structural guides on a frame assembly of the milling device(block 196). As noted above, the structural guides enable the millingdevice to engage structural features on the inner surface of the casingof the gas turbine engine to maintain an axial position (e.g., relativeto the longitudinal axis of the casing) of the milling device. Incertain embodiments, if structural guides are already coupled to themilling device, the structural guides may be changed out for another setof structural guides having a different size and/or shape. The method194 also includes adjusting a size of the frame assembly to attach themilling device to the inner surface of the casing utilizing thestructural features on the inner surface (block 198). The method 194further includes machining the slot into the inner surface of the casingutilizing the milling device (block 200). The milling device is pushedin a circumferential direction about the inner surface of the casing.

Technical effects of the disclosed embodiments include providing amilling device that is configured to machine a circumferential slotalong an inner surface of a casing of a gas turbine engine. Thearchitecture of the milling device enables it to be adapted to andutilized on the inner surface of any casing (e.g., circular orsemi-circular casing) of a gas turbine engine that has casing featuresnear an area to be milled. The milling device also enables precisealignment of the milling or cutting tool to create the circumferentialslot utilizing the casing features. The milling device may even beutilized on casings that are damaged, warped, or worn. In addition, themilling device is highly transportable due to its small size and lightweight and may be utilized by a single person to machine the slot.

This written description uses examples to disclose the disclosed subjectmatter, including the best mode, and also to enable any person skilledin the art to practice the disclosed subject matter, including makingand using any devices or systems and performing any incorporatedmethods. The patentable scope of the disclosed subject matter is definedby the claims, and may include other examples that occur to thoseskilled in the art. Such other examples are intended to be within thescope of the claims if they have structural elements that do not differfrom the literal language of the claims, or if they include equivalentstructural elements with insubstantial differences from the literallanguage of the claims.

1. A milling device for machining a slot into an inner surface of acasing for a gas turbine engine, comprising: a frame assembly comprisinga plurality of structural guides configured to engage structuralfeatures on the inner surface of the casing to maintain an axialposition of the milling device relative to a longitudinal axis of thecasing; and a milling cutter coupled to the frame assembly; wherein themilling device is configured to be displaced in a circumferentialdirection relative to the longitudinal axis to machine the slot, via themilling cutter, along the inner surface of the casing in thecircumferential direction.
 2. The milling device of claim 1, whereineach structural guide of the plurality of structural guides comprises anL-shape.
 3. The milling device of claim 1, wherein the frame assembly isconfigured to be interchangeably coupled to different sets of structuralguides, and each different set of structural guides is configured toengage structural features of different sizes, shapes, or a combinationthereof, on the inner surface of the casing.
 4. The milling device ofclaim 1, wherein the frame assembly is adjustable in size.
 5. Themilling device of claim 4, wherein the frame assembly comprises a pairof rails coupled to a pair of bars, and a position of each rail of thepair of rails is adjustable along a length of the pair of bars.
 6. Themilling device of claim 4, comprising a plurality of spring loaded pinson the pair of rails, wherein the plurality of spring loaded pins isconfigured to provide a supporting force in a direction perpendicular tothe longitudinal axis of the casing and wherein each spring loaded pinof the plurality of spring loaded pins is frictionless to enablemovement of the milling device in the circumferential direction.
 7. Themilling device of claim 1, comprising a plate coupled to the frameassembly, wherein the milling cutter is coupled to the frame assemblyvia the plate.
 8. The milling device of claim 7, wherein a position ofthe milling cutter on the plate is adjustable in an axial directionrelative to the longitudinal axis of the casing.
 9. The milling deviceof claim 1, comprising rollers to enable movement of the milling devicein the circumferential direction.
 10. The milling device of claim 1,wherein the structural features on the inner surface of the casingcomprise slots extending in the circumferential direction.
 11. A sledmilling device, comprising: a frame assembly; a milling cutter coupledto the frame assembly; and a bearing support configured to interfacewith an inner surface of a casing of a gas turbine engine, to provide asupporting force in a direction perpendicular to a longitudinal axis ofthe casing, and to enable movement of the sled milling device in acircumferential direction relative to the longitudinal axis; wherein thesled milling device is configured to be displaced in the circumferentialdirection to machine a slot, via the milling cutter, along the innersurface of the casing in the circumferential direction.
 12. The sledmilling device of claim 11, wherein the bearing support is disposed on asurface of the frame assembly that faces the inner surface of thecasing.
 13. The sled milling device of claim 11, wherein the bearingsupport comprises a plurality of frictionless spring loaded pins. 14.The sled milling device of claim 11, wherein the frame assemblycomprises a plurality of structural guides configured to engagestructural features on the inner surface of the casing to maintain anaxial position of the milling device relative to the longitudinal axisof the casing.
 15. The sled milling device of claim 14, wherein eachstructural guide of the plurality of structural guides comprises anL-shape.
 16. The sled milling device of claim 14, wherein the frameassembly is configured to be interchangeably coupled to different setsof structural guides, and each different set of structural guides isconfigured to engage structural features of different sizes, shapes, ora combination thereof, on the inner surface of the casing.
 17. The sledmilling device of claim 11, comprising a plate coupled to the frameassembly, wherein the milling cutter is coupled to the frame assemblyvia the plate.
 18. The milling device of claim 17, wherein a position ofthe milling cutter on the plate is adjustable in an axial directionrelative to the longitudinal axis of the casing.
 19. A milling systemfor machining a slot into an inner surface of a casing for a gas turbineengine, comprising: a sled milling device comprising a frame assemblyand a milling cutter, wherein the sled milling device is configured tobe displaced in a circumferential direction relative to a longitudinalaxis of the casing to machine the slot, via the milling cutter, alongthe inner surface of the casing in the circumferential direction,wherein the frame assembly is configured to be interchangeably coupledto different sets of structural guides, wherein each set of structuralguides comprises a different size, shape, or a combination thereof, toenable the sled milling device to engage different structural featureson the inner surface of the casing to maintain an axial position of themilling device relative to a longitudinal axis of the casing; and thedifferent sets of structural guides.
 20. The milling system of claim 19,comprising a bearing support coupled to the frame assembly andconfigured to interface with the inner surface of the casing, to providea supporting force in a direction perpendicular to the longitudinal axisof the casing, and to enable movement of the sled milling device in acircumferential direction relative to the longitudinal axis.